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Roof Rail marks puzzling

Posted: Wed Apr 08, 2015 12:33 pm
by Gel
Rear N/S section of roof rack rail:Image shows some "scratches" I've just seen on washing car.However passing my thumbnail over, they're totally smooth and topcoat surface is not damaged. I'm wondering if in fact it's the paint crazing; anyone else seen before I ask dealer?

Roof Rail marks puzzling

Posted: Wed Apr 08, 2015 3:10 pm
by DaveBerlin
Gel, I do not think that these Roof Rails are painted they are most likely Surface Treated with for example the "Anodising" Process. The surface treatment is so thin that if these were deep scratches you would indeed feel them with a finger nail. It is highly likely that this has happened by abrasion (cleaning methods) or the defect was there originally, treated and now the scratches are appearing. Take a look at this :


Anodising is an electrochemical technique most usually applied to aluminium and its alloys. These are treated to form a structured surface oxide layer. This layer has anti-corrosion and decorative properties.
The anodising techniques applied on aluminium are divided into:
Sulphuric acid-anodising / Hard anodizing / Chromium acid anodising.
Anodising of aluminium is frequently applied. Since the anodised layer is thin and transparent, surface damage and scrapes are easily visible. Before anodising aluminium components must be treated carefully in order to prevent damage.
Aluminium anodising: properties : The layer thickness of an anodising layer made in a (standard) sulphuric acid anodising bath can be selected to be between 1 and approx. 30 micrometer. Hard anodising gives layers of approx. 5 up to 100-150 micrometer thick (dependent of the type of hard anodising bath).The layer grows partially (approx. 60%) out of the substrate so that an anodising layer of 20 micrometer will give rise to an extra thickness of the component of 8 micrometer.
Anodised aluminium can be given many different colours. If coloured with inorganic dyes, they show very reproducible and stable colours (organic dyes are less stable).Sulphuric acid anodising treatment strongly reduces the fatigue strength of aluminium so that this process is less suitable for components subjected to fatigue. Chromium acid anodising is better suited for fatigue resistance applications. Anodising layers are also suited as substrate for adhesive or for organic top layers. They are not very resistant to hydrogen fluoride containing cleaning products. Also strong alkaline solutions and acids attack anodising layers. The corrosion resistance of sulphuric acid anodising layers is caused by sealing of the pores with aluminium hydrate.

If you have a Plating Shop in your area try dropping in and asking them their opinion - asking costs nothing. It looks like you have luck though that it is one end section which should be interchangeable by Nissan hopefully - I hope this helps I could well be wrong though Dave

Roof Rail marks puzzling

Posted: Wed Apr 08, 2015 3:17 pm
by Gel
Dave, thanks.Defects only showed at this week's washing ceremony; I don't use car washes, and same method used to clean my QQ as I have since new. As you say hopefully end bit can just be replaced under warranty. If I have grief there, I could use my Scratch & Dent insurance policy to rectify.

Roof Rail marks puzzling

Posted: Wed Apr 08, 2015 9:11 pm
by duncho
Dave, scratches shown on the photo are just plastic covers. When you take them off you will find screws that goes through the roof. It seems really heavily "scratched". On one of mine (driver side) there are stains on the paint as it wasn't properly degreased before they sprayed it.

Roof Rail marks puzzling

Posted: Wed Apr 08, 2015 9:47 pm
by Gel
Duncho, thanks for that. Does it just snap off then?

Roof Rail marks puzzling

Posted: Wed Apr 08, 2015 9:53 pm
by duncho
Yes, just be careful not to break plastic retainers.

Roof Rail marks puzzling

Posted: Thu Apr 09, 2015 7:44 am
by Deleted User 759
Maybe catsI have found a few scratches on my bonnet from my neighbours beloveds! Fecking things....

Roof Rail marks puzzling

Posted: Thu Apr 09, 2015 9:13 am
by jonceebee
Dan and Steve's comments are probably right. I had a similar problem on an earlier car where the plastic screw covers as Dan says got damages with scratches. This was down to a neighbours cat trying to get a grip when jumping on the roof. I took the cover off went to Halfords and found the nearest colour in spray form, rubbed down and res-prayed. Looked like new afterwards.The anodised metal parts do not scratch so easily.

Roof Rail marks puzzling

Posted: Fri Apr 10, 2015 2:53 pm
by DaveBerlin
Gel, what's the News on this part, cats ! the marks looked like it came from a Lion. So I was at the Dealer today and took a look in the Store PC with the Store Guy and all that we could find was a Complete LH / RH Assy no individual parts. The Part Nos were if this helps #73820-4EA0A RH & #73821-4EA0A LH and priced at wait for it a‚¬372.
I expect someone will pop up with a cheaper offer - Dave

Roof Rail marks puzzling

Posted: Fri Apr 10, 2015 4:49 pm
by Gel
Visiting dealer next week. See my pics have disappeared above, something awry regards rendering on forum today, as I noticed your original post on your interior lights had gone too.